如何使用 select() 为套接字设置定时器？

Question

我目前正在使用 Winsock2 来测试与多个本地 telnet 服务器的连接，但是如果服务器连接失败，default Winsock client 会永远超时。

我在其他帖子上看到select()可以设置连接部分的超时时间，setsockopt()和timeval可以让接收部分的代码超时，但是我也不知道如何实施。我从其他答案中 copy/pasted 得到的代码片段对我来说似乎总是失败。

如何在默认客户端代码中使用这两个函数？或者，如果无法在默认客户端代码中使用这些函数，有人可以指导我如何正确使用这些函数吗？


#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <ctime>

// Need to link with Ws2_32.lib, Mswsock.lib, and Advapi32.lib
#pragma comment (lib, "Ws2_32.lib")
#pragma comment (lib, "Mswsock.lib")
#pragma comment (lib, "AdvApi32.lib")


#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "23"



int __cdecl main(int argc, char** argv)
{
    WSADATA wsaData;
    SOCKET ConnectSocket = INVALID_SOCKET;
    struct addrinfo* result = NULL,
        * ptr = NULL,
        hints;
    const char* sendbuf = "this is a test";
    char recvbuf[DEFAULT_BUFLEN];
    int iResult;
    int recvbuflen = DEFAULT_BUFLEN;

    // Validate the parameters
    if (argc != 2) {
        printf("usage: %s server-name\n", argv[0]);
        return 1;
    }

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed with error: %d\n", iResult);
        return 1;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    /*
    struct timeval timeout;
    timeout.tv_sec = 10;
    timeout.tv_usec = 0;

    if (setsockopt(ConnectSocket, SOL_SOCKET, SO_RCVTIMEO, (char*)&timeout,
        sizeof(timeout)) < 0) {
        printf("setsockopt failed\n");
    }
    */

    




    // Resolve the server address and port
    iResult = getaddrinfo(argv[1], DEFAULT_PORT, &hints, &result);
    if (iResult != 0) {
        printf("getaddrinfo failed with error: %d\n", iResult);
        WSACleanup();
        return 1;
    }





    // Attempt to connect to an address until one succeeds
    for (ptr = result; ptr != NULL; ptr = ptr->ai_next) {

        // Create a SOCKET for connecting to server
        ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype,
            ptr->ai_protocol);
        if (ConnectSocket == INVALID_SOCKET) {
            printf("socket failed with error: %ld\n", WSAGetLastError());
            WSACleanup();
            return 1;
        }

        // Connect to server.
        iResult = connect(ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
        if (iResult == SOCKET_ERROR) {
            closesocket(ConnectSocket);
            ConnectSocket = INVALID_SOCKET;
            continue;
        }
        break;
    }

    freeaddrinfo(result);

    if (ConnectSocket == INVALID_SOCKET) {
        printf("Unable to connect to server!\n");
        WSACleanup();
        return 1;
    }

    // Send an initial buffer
    iResult = send(ConnectSocket, sendbuf, (int)strlen(sendbuf), 0);
    if (iResult == SOCKET_ERROR) {
        printf("send failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    printf("Bytes Sent: %ld\n", iResult);

    // shutdown the connection since no more data will be sent
    iResult = shutdown(ConnectSocket, SD_SEND);
    if (iResult == SOCKET_ERROR) {
        printf("shutdown failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    // Receive until the peer closes the connection
    do {

        iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
        if (iResult > 0)
            printf("Bytes received: %d\n", iResult);
        else if (iResult == 0)
            printf("Connection closed\n");
        else
            printf("recv failed with error: %d\n", WSAGetLastError());

    } while (iResult > 0);

    // cleanup
    closesocket(ConnectSocket);
    WSACleanup();

    return 0;
}

Answer 1

select() can set a timeout for the connection part.

是的，但前提是你在调用connect()之前将套接字设置为非阻塞模式，这样connect()立即退出，然后代码可以使用select()等待连接操作完成时要报告的套接字。但是显示的代码并没有这样做。

setsockopt() with timeval can timeout the receiving portion of the code

是的，不过 select() 也可用于使读取操作超时。只需先调用 select()，然后仅当 select() 报告套接字可读（有待读数据）时才调用 recv()。

尝试这样的事情：

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <stdio.h>
#include <ctime>

// Need to link with Ws2_32.lib, Mswsock.lib, and Advapi32.lib
#pragma comment (lib, "Ws2_32.lib")
#pragma comment (lib, "Mswsock.lib")
#pragma comment (lib, "AdvApi32.lib")

#define DEFAULT_BUFLEN 512
#define DEFAULT_PORT "23"

int __cdecl main(int argc, char** argv)
{
    WSADATA wsaData;
    SOCKET ConnectSocket = INVALID_SOCKET;
    struct addrinfo *result = NULL,
        *ptr = NULL,
        hints;
    const char* sendbuf = "this is a test";
    char recvbuf[DEFAULT_BUFLEN];
    int iResult;
    int recvbuflen = DEFAULT_BUFLEN;

    // Validate the parameters
    if (argc != 2) {
        printf("usage: %s server-name\n", argv[0]);
        return 1;
    }

    // Initialize Winsock
    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0) {
        printf("WSAStartup failed with error: %d\n", iResult);
        return 1;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    // Resolve the server address and port
    iResult = getaddrinfo(argv[1], DEFAULT_PORT, &hints, &result);
    if (iResult != 0) {
        printf("getaddrinfo failed with error: %d\n", iResult);
        WSACleanup();
        return 1;
    }

    // Attempt to connect to an address until one succeeds
    for (ptr = result; ptr != NULL; ptr = ptr->ai_next) {

        // Create a SOCKET for connecting to server
        ConnectSocket = socket(ptr->ai_family, ptr->ai_socktype, ptr->ai_protocol);
        if (ConnectSocket == INVALID_SOCKET) {
            printf("socket failed with error: %ld\n", WSAGetLastError());
            WSACleanup();
            return 1;
        }

        // put the socket into non-blocking mode just for connect()
        int iMode = 1;
        iResult = ioctlsocket(ConnectSocket, FIONBIO, &iMode);
        if (iResult == SOCKET_ERROR)
            closesocket(ConnectSocket);
            ConnectSocket = INVALID_SOCKET;
            continue;
        }

        // Connect to server.
        iResult = connect(ConnectSocket, ptr->ai_addr, (int)ptr->ai_addrlen);
        if (iResult == SOCKET_ERROR) {
            if (WSAGetLastError() != WSAEWOULDBLOCK) {
                closesocket(ConnectSocket);
                ConnectSocket = INVALID_SOCKET;
                continue;
            }

            // wait for the connect to finish
            fd_set fds;
            FD_ZERO(&fds);
            FD_SET(ConnectSocket, &fds);

            struct timeval timeout;
            timeout.tv_sec = 10;
            timeout.tv_usec = 0;

            iResult = select(0, NULL, &fds, NULL, &timeout);
            if (iResult <= 0) {
                closesocket(ConnectSocket);
                ConnectSocket = INVALID_SOCKET;
                continue;
            }
        }

        // put the socket back into blocking mode
        iMode = 0;
        iResult = ioctlsocket(ConnectSocket, FIONBIO, &iMode);
        if (iResult == SOCKET_ERROR) {
            closesocket(ConnectSocket);
            ConnectSocket = INVALID_SOCKET;
            continue;
        }

        break;
    }

    freeaddrinfo(result);

    if (ConnectSocket == INVALID_SOCKET) {
        printf("Unable to connect to server!\n");
        WSACleanup();
        return 1;
    }

    struct timeval timeout;
    timeout.tv_sec = 10;
    timeout.tv_usec = 0;

    // set a read timeout
    if (setsockopt(ConnectSocket, SOL_SOCKET, SO_RCVTIMEO, (char*)&timeout, sizeof(timeout)) == SOCKET_ERROR) {
        printf("setsockopt failed\n");
    }

    // Send an initial buffer
    iResult = send(ConnectSocket, sendbuf, (int)strlen(sendbuf), 0);
    if (iResult == SOCKET_ERROR) {
        printf("send failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    printf("Bytes Sent: %ld\n", iResult);

    // shutdown the connection since no more data will be sent
    iResult = shutdown(ConnectSocket, SD_SEND);
    if (iResult == SOCKET_ERROR) {
        printf("shutdown failed with error: %d\n", WSAGetLastError());
        closesocket(ConnectSocket);
        WSACleanup();
        return 1;
    }

    // Receive until the peer closes the connection
    do {
        /*
        fd_set fds;
        FD_ZERO(&fds);
        FD_SET(ConnectSocket, &fds);

        struct timeval timeout;
        timeout.tv_sec = 10;
        timeout.tv_usec = 0;

        iResult = select(0, &fds, NULL, NULL, &timeout);
        if (iResult <= 0) {
            if (iResult == SOCKET_ERROR)
                printf("select failed with error: %d\n", WSAGetLastError());      
            else
                printf("select timed out\n");
            break;
        }
        */

        iResult = recv(ConnectSocket, recvbuf, recvbuflen, 0);
        if (iResult > 0)
            printf("Bytes received: %d\n", iResult);
        else if (iResult == 0)
            printf("Connection closed\n");
        else if (WSAGetLastError() == WSAETIMEDOUT)
            printf("recv timed out\n");
        else
            printf("recv failed with error: %d\n", WSAGetLastError());

    } while (iResult > 0);

    // cleanup
    closesocket(ConnectSocket);
    WSACleanup();

    return 0;
}

如何使用 select() 为套接字设置定时器？

How to use select() to set a timer for sockets?

c++

winsock2